Impaired surface marker expression in stimulated Epstein-Barr virus transformed lymphoblasts from Barth Syndrome patients

Primary B lymphocytes rapidly respond to lipopolysaccharide (LPS) and cytosine linked to a guanine by a phosphate bond deoxyribonucleic acid (CpG DNA) stimulation to promote adaptive immune function through increased surface marker expression. Here we examined expression of surface markers in LPS and CpG DNA stimulated Epstein-Barr virus transformed B lymphoblasts from control and BTHS patients with different mutations. The percentage of cluster of differentiation (CD) positive cells including CD38 + , CD138 + , CD80 + surface expression and programmed cell death protein 1 (PD1 +) surface expression was similar between control and BTHS lymphoblasts incubated plus or minus LPS. The percentage of CD24 + , CD38 + and CD138 + cells was similar between control and BTHS lymphoblasts incubated plus or minus CpG DNA. CD27 + surface marker expression was reduced in both BTHS lymphoblasts and controls incubated with CpG DNA and PD1 + surface marker expression was higher in BTHS cells compared to controls but was unaltered by CpG DNA treatment. Thus, Epstein-Barr virus transformed control and BTHS lymphoblasts fail to increase selected surface markers upon stimulation with LPS and exhibit variable surface marker expression upon stimulation with CpG DNA. Since B lymphocyte surface marker expression upon activation is involved in B cell proliferation and differentiation, cell–cell interaction and the adaptive immune response, we suggest that caution should be exercised when interpreting immunological data obtained from Epstein-Barr virus transformed BTHS cells. Based upon our observations in control cells, our conclusions may be more broadly applicable to other diseases which utilize transformed B lymphocytes for the study of immune biology.


Primary B lymphocytes rapidly respond to lipopolysaccharide (LPS) and cytosine linked to a guanine by a phosphate bond deoxyribonucleic acid (CpG DNA) stimulation to promote adaptive immune function through increased surface marker expression. Here we examined expression of surface markers in LPS and CpG DNA stimulated Epstein-Barr virus transformed B lymphoblasts from control and BTHS patients with different mutations. The percentage of cluster of differentiation (CD) positive cells including CD38 + , CD138 + , CD80 + surface expression and programmed cell death protein 1 (PD1 +) surface expression was similar between control and BTHS lymphoblasts incubated plus or minus LPS. The percentage of CD24 + , CD38 + and CD138 + cells was similar between control and BTHS lymphoblasts incubated plus or minus CpG DNA. CD27 + surface marker expression was reduced in both BTHS lymphoblasts and controls incubated with CpG DNA and PD1 + surface marker expression was higher in BTHS cells compared to controls but was unaltered by CpG DNA treatment. Thus, Epstein-Barr virus transformed control and BTHS lymphoblasts fail to increase selected surface markers upon stimulation with LPS and exhibit variable surface marker expression upon stimulation with CpG DNA. Since B lymphocyte surface marker expression upon activation is involved in B cell
proliferation and differentiation, cell-cell interaction and the adaptive immune response, we suggest that caution should be exercised when interpreting immunological data obtained from Epstein-Barr virus transformed BTHS cells. Based upon our observations in control cells, our conclusions may be more broadly applicable to other diseases which utilize transformed B lymphocytes for the study of immune biology.
Barth Syndrome (BTHS) is a rare X-linked genetic disease caused by a mutation in the TAFAZZIN gene which codes for the cardiolipin (CL) transacylase protein tafazzin 1-3 . Tafazzin remodels nascent de novo synthesized CL into a form of CL found in the tissue specific mitochondrial membrane 4 . As the signature lipid of mitochondria, CL is required to support many mitochondrial functions including energy production required for adaptive immunity of B lymphocytes 5,6 . Although cardiomyopathy is the major cause of mortality in BTHS, many patients suffer from severe infections due to neutropenia 1,2 .
Several laboratories, including our own, have utilized Epstein-Barr virus transformed B lymphoblasts from patients for the study of BTHS pathology [7][8][9][10][11] . The rationale for the use of these cells is that they are easy to maintain in culture and the transformed nature of these cells makes them readily amenable to experimental manipulation. In addition, they are representative of the specific mutation of a given patient. However, studies have also indicated that Epstein-Barr virus transformation of human B lymphocytes may hinder host immune function 12 . B lymphoblasts express Toll-like receptors (TLRs) including TLR4 which can be stimulated with lipopolysaccharide (LPS) 13 . In addition, cytosine linked to a guanine by a phosphate bond deoxyribonucleic acid (CpG DNA) activates human B lymphocytes through TLR9 regardless of whether the DNA is in the form of genomic bacterial DNA or in the form of a synthetic oligodeoxynucleotide 14

Materials and methods
Epstein-Barr virus transformed human control lymphoblasts and Epstein-Barr virus transformed BTHS lymphoblasts were obtained from the Coriell Institute for Medical Research (Camden, NJ, USA). The cells that were used in the study are outlined in Table 1 Cell culture and stimulation. All

Cell viability and surface marker expression analysis. Briefly, after 24 h of stimulation with LPS or
CpG DNA, the lymphoblasts were centrifuged at 1400 rpm for 10 min. The pellets were washed with PBS and suspended in 100 µl of PBS. Lymphoblasts were stained with propidium iodide (5 µg/ml) for 5 min in the dark at 4 °C. This was followed by flow cytometry analysis. Surface marker expression was measured in untreated and stimulated lymphoblasts by staining the cell surface with anti-CD19-APC, anti-CD24-BV421, anti-CD27-perCP-CY5.5, anti-CD38-APC-H7, anti-CD138-PE, anti-CD80 PE-A, and anti-PD1-APC as per the manufacturer's instructions. Cells were then analyzed by flow cytometry at the Flow Cytometry Core Facility in the Rady Faculty of Health Sciences, University of Manitoba, using a BD FACS Canto II instrument. FlowJo software was used for data analysis.
Statistical analysis. All data are expressed as mean ± SD. Comparison between two groups was performed by using Two tailed unpaired Student's t test, and comparison between multiple groups was achieved using oneway analysis of variance (ANOVA) followed by Tukey's post-hoc multiple comparison test. A p value of < 0.05 was considered statistically significant.

Cell viability is maintained in Epstein-Barr virus transformed human control and BTHS B lymphoblasts after stimulation.
Initially we examined viability of LPS and CpG DNA treated control and BTHS B lymphoblasts. Epstein-Barr virus transformed B lymphoblasts from 3 control patients and 3 BTHS patients with different mutations were incubated for 24 h with 10 µg/ml LPS or 5 µM CpG DNA then stained with propidium iodide and flow cytometry performed to assess cell viability. We observed that cell viability was maintained in both control and BTHS lymphoblasts incubated with 10 µg/ml LPS (Fig. 1a) or 5 µM CpG DNA (Fig. 1b) (Fig. 2a-c). In addition, the percentage of CD80 + and PD1 + surface expression was similar between control and BTHS B lymphoblasts incubated minus or plus LPS for 24 h (Fig. 3a-c). Thus, selected surface marker expression in Epstein-Barr virus transformed human control and BTHS B lymphoblasts was refractory to stimulation with LPS.

Epstein-Barr virus transformed human control and BTHS B lymphoblasts show variable surface marker expression upon CpG DNA stimulation.
Control and BTHS B lymphoblasts were incubated minus or plus 5 µM CpG DNA for 24 h and expression of the surface markers CD24 + , CD38 + , CD138 + , CD27 + and PD1 + determined. The percentage of CD24 + and CD38 + was similar between control and BTHS B lymphoblasts incubated minus or plus 5 µM CpG DNA for 24 h (Fig. 4a-c). In contrast, CD27 + surface marker expression was reduced in both control and BTHS B lymphoblasts incubated with 5 µM CpG DNA for 24 h. The percentage of CD138 + expression was similar between control and BTHS B lymphoblasts incubated minus or plus 5 µM CpG DNA for 24 h (Fig. 5a-c). In contrast, the percentage of PD1 + expression was higher in BTHS cells compared to controls but was unaltered by incubation with 5 µM CpG DNA for 24 h. Thus, Epstein-Barr virus transformed human control and BTHS B lymphoblasts showed variable selected surface marker expression upon CpG DNA stimulation.

Discussion
In this study we examined whether Epstein-Barr virus transformed control and BTHS B lymphoblasts expressed surface markers indicative of classical B lymphocyte activation upon LPS or CpG DNA stimulation. Surprisingly, our results clearly demonstrate that Epstein-Barr virus transformed human control and BTHS B lymphoblasts are refractory to selected surface marker expression upon stimulation with LPS and exhibit variable selected surface marker expression upon stimulation in response to CpG DNA. CD24 is expressed at the surface of activated B lymphocytes and is required for B cell development and plays a key role in cell-cell adhesion 15 . In addition, CD24 expression on B cells is required for T cell co-stimulation in CD4 T-cell mediated clonal expansion 16 . CD38 is a key surface marker for B cell activation and plays an important role in B cell proliferation and regulation 17 . Previous studies showed that deficiency of CD38 expression resulted in inhibition of the immune response and increased susceptibility to infections 18 . CD138 is a specific surface marker of plasma cells which are required for long-term humoral immunity 19 . Upon stimulation, B cells differentiate into antibody secreting cells and upregulate CD138 on their surface which enhances antibody secreting cell maturation and accumulation 20 . CD80 is expressed in activated B cells and provides a co-stimulatory signal necessary for T cell activation 21   www.nature.com/scientificreports/ and that transformation may hinder normal immune function 12 . We recently demonstrated that isolated naïve primary murine B lymphocytes stimulated with LPS readily increased surface marker expression and that tafazzin deficiency in these cells markedly impaired surface marker expression upon stimulation with LPS 22 . The lack of elevated surface marker expression in human control and BTHS lymphoblasts in response to LPS, coupled with the fact that these surface markers were readily detectable in unstimulated cells, indicate that these cells exhibit impaired responsiveness to LPS-mediated activation. CD27 is a B lymphocyte memory marker and a co-stimulatory immune molecule which belongs to the tumor necrosis factor receptor superfamily 23 . CD27 surface marker expression plays an important role in immunoglobulin synthesis and in regulating B cell activation through binding with CD70 on activated B and T lymphocytes www.nature.com/scientificreports/ and modulates induction of apoptosis 24,25 . PD1 surface marker expression down regulates the immune system to limit inflammation by modulating T-cell activity 26 . For example, PD1 expressed on the surface of activated B cells inhibited CD4 + and CD8 + T cell proliferation 27 . In addition, inhibition of the PD1 pathway resulted in increased B cell activation, proliferation and secretion of inflammatory cytokines 28 . Intriguingly, CD27 surface expression was reduced in both control and BTHS B lymphoblasts stimulated with CpG DNA. In contrast, PD1 surface expression was higher in BTHS cells compared to controls but was unaltered by stimulation with CpG DNA. These data suggest that Epstein-Barr virus transformed human control and BTHS B lymphoblasts exhibit variability in surface marker expression upon CpG DNA stimulation.  www.nature.com/scientificreports/ The significance of our observations is currently unknown. However, Epstein-Barr virus infection of human B lymphocytes was recently shown to promote major modifications of alternative splice variant expression which may impact on cell fate determination 29 . In addition, the differences in gene expression patterns observed between Epstein-Barr virus transformed and normal lymphocytes 12,30 , coupled with our observation of impaired B cell surface marker expression, could potentially influence transformed B lymphocyte function when infection is mimicked through LPS-or CpG DNA-mediated activation. Thus, the Epstein-Barr virus transformed BTHS lymphoblast phenotype may exhibit a lack of responsiveness to pro-inflammatory stimuli and potentially Hence, impaired B cell activation in Epstein-Barr virus transformed BTHS lymphoblasts could potentially attenuate neutrophil recruitment. Another conclusion from our study, derived from the behavior of the controls, is that it can be assumed that the effects are not necessarily limited to BTHS but are more broadly applicable to other diseases which utilize Epstein-Barr virus transformed B lymphocytes for the study of immune pathology. In summary, based upon our observations we suggest that caution should be exercised when interpreting immunological data obtained from Epstein-Barr virus transformed lymphoblasts.